Asa Gray (November 18, 1810 - January 30, 1888) is considered the most important American botanist of the 19th century.

He was instrumental in unifying the taxonomic knowledge of the plants of North America. Of Gray's many works on botany, the most popular was his Manual of the Botany of the Northern United States, from New England to Wisconsin and South to Ohio and Pennsylvania Inclusive. This book, known simply as Gray's Manual, has gone through a number of editions with botanical illustrations by Isaac Sprague, and remains a standard in the field.

He was born in Sauquoit, New York in 1810, and became an M.D. in 1831 However, he relinquished medicine for botany, and in 1842 was appointed professor of natural history at Harvard University, a post he retained until 1873. Through the donation of an immense book and plant collection numbering in the thousands, he effectively created the botany department at Harvard; the Gray Herbarium is named after him.

He was a pupil of John Torrey, with whom he worked closely; they published the Flora of North America together, the first of many of Gray's works.

Corresponding with Charles Darwin, Gray was helpful in providing information for the development of Darwin's theory on The Origin of Species. He was a staunch supporter of Darwin in America, and collected together a number of his own writings to produce an influential book, Darwiniana. These essays argued for a conciliation between Darwinian evolution and the tenets of orthodox Protestant Christianity, at a time when many on both sides perceived the two as mutually exclusive.

The Asa Gray Award, the highest award of the American Society of Plant Taxonomists, was established in 1984 to honor a living botanist for career achievements.